1. Field of the Invention
This invention relates to apparatus for gathering data from which a topographic map can be generated, and more particularly to gathering data with respect to terrain that is covered with foliage by traversing such terrain with an aircraft equipped with data gathering apparatus.
2. Description of the Prior Art
U.S. Pat. No. 4,050,067 discloses an airborne microwave path modeling system in which radar equipment is flown between two microwave towers, and data indicative of the terrain profile between the towers is stored and plotted. Simultaneously with storage of the radar data, information concerning the altitude of the plane and ambient barometric pressure, humidity and temperature is recorded to afford calculation of atmospheric absorbtion so that a corrected plot of the microwave reflectivity of the terrain can be generated.
U.S. Pat. No. 2,845,620 discloses an aerial mapping and profiling system in which a microwave reflector is swept on a path transverse to the direction of travel over the surface of the earth. The output of each sweep is recorded photographically, and the system includes a plan position indicator which cooperates with two or more ground based stations to produce signals indicating the position of the microwave reflector over the earth surface. The position signals are recorded on film.
U.S. Pat. No. 4,101,891 discloses a surface roughness measuring system in which an aircraft mounted radar system is flown over ocean waves or rough terrain to determine the roughness thereof. The data acquired by the system is recorded on film.
U.S. Pat. No. 3,727,219 discloses an interferometer null multiplication technique and apparatus having a pair of airborne receiving antennas and a film for recording the signals received by the antennas in seperable form. The recorded signals interfere with one another at a null which is representative of the angle between a radar beam and the surface of the terrain over which the antennas are flown.
U.S. Pat. No. 3,680,086 discloses a ground mapping radar system having an airborne directionally scanning ranging system which creates a display. The system also includes a navigation system and a vehicle motion compensator which are applied to the display to compensate for aircraft movement.
U.S. Pat. No. 3,213,415 discloses an airborne contour-sensing radar employing a high frequency radar signal for sensing differences in height and reflectivity of objects over which the radar is flown. The radar data obtained by the system is reproduced on a display in the aircraft.
In a paper titled "High Resolution Measurements of Snowpacked Stratigraphy Using a Short Radar Pulse" by Vickers and Rose, Proceedings of the Eighth International Symposium on Remote Sensing of Environment, October 1972, Ann Arbor, Mich., there is described measurements of the thickness and the density of a snowpack by use of radar waves directed at the snowpack from an antenna supported on a ground surface traversing vehicle. The paper reports on the correlation between dielectric losses in the snow and frequency from a range of 10.sup.3 to 10.sup.10 Hz.
A paper entitled "Radio Echo Sounding of Temperate Glaciers at Frequencies of 1 to 5 MHz" by Watts et al. presented at the Symposium of Remote Sensing in Glaciology at Cambridge, England, September 1974, describes a vehicle mounted radar system which can traverse a glacier and produce data indicative of the thickness of the glacier.